Spark plug



July 14, 1942.

R. ABELL SPARK mue Filed-Jan. 17, 19:59v

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INVENTOR Roan flbeZZ B ATTORNEY Patented July 14,1942

UNITED STATES PATENT OFFICE SPARK PLUG Ronin Abell, Chatham, Mass.

Application January 17, 1939, Serial No. 251,285

4 Claims.

, at a given voltage or the production or a satisfactory volume of spark at a reducedvoltage as compared with other4 spark plugs upon the market.

With the above and other objects in view I have illustrated in the accompanying drawing preferred embodiments of my invention and wherein:

Fig. 1 shows a central vertical section through a simpliiled form of my invention.

Fig. 2 represents a lcentral vertical section of one of my spark plugs, the essential features of which are like those of Fig. 1 and in addition includes a protective covering for the insulating member. p

Fig. 3 is a slightly modified form of the construction shown in Fig. 2, the principal difference being in the formation of the lower or sparking end oi the plug, and

Fig. 4 again shows a slightly modified form of construction wherein the end of the electrode ilnishes below the insulating tube and flush with the lower end of the metal shell.

By the use of a thin-walled tube of heat resisting glass and the employment of cement as between the said glass and the electrode, a more eiilcient plug is produced, better adapted to withstand severe conditions oi use for much longer periods or time than other spark plugs now on the market.

Referring to the characters of reference marked on the drawing, I0 represents an outer steel shell or supporting member, the main body oi which may have an enlarged shouldered surtace II to form a head for the application of a wrench by means of which the plug may be screwed into thev cylinder head of a gasoline motor. The reduced lower portion of this shell member is threaded as at I2 to threadably engage a tapped hole in a cylinded head, not shown. The central portion of this shell is bored torreceive an insulating member I3 that may finish ilush at its lower end with the threaded lower end portion I2 of the member I 0. In Fig. 1 the insulating member I3 extends above the member I0 and is provided with a bore therethrough to receive an electrode I4 which extends through the length of the insulating member and is provided with a washer I5 and a riveted head I6 to support the electrode against any tendency to move upward and outward. In this connection it will also be noted that a shoulder Il is formed on the member I3 better to hold it in position as against the shouldered shell. A terminal I8 is threadably attached to the upper end portion of the electrode for the attachment of ignition wires, not shown.

I also provide a filling of cement I9 around the electrode as between it and the tubular insulat- .ing member I3 to insure a complete closure as between thetwo parts so as to prevent gas leakage therethrough, from the motor. A filling of cement 20 is also placed between the insulating member and the shell where the former extends through the latter to prevent leakage of gas as in the previous instance. In the form shown in Figs. 2, 3 and 4, where a protective covering 2I of suitable insulating material surrounds the insulating member I3, the shell in addition to the lower reduced threaded portion II is providedwith an upwardly extended reduced central portion 22 that is also threaded as at 23 for the attachment of the protective covering 2 being appliedln spaced relation to the tubular insulating member. The upper inner end of this covering 2I is 'threaded to receive the threaded terminal Y I8 which is threadably attached as in Fig. l to the threaded portion of said insulator.

This member 2| is of a general cylindrical form having a tapered outer surface and a central hole 24 to surround the tubular insulating member I3. As shown in Figs. 2, 3 and 4, the terminal may be screwed into the covering 2t and seated against the upper end of the electrode while the lower end of the electrode as seen in Figs. 2 and 3 iinishes flush with the lower end of the tubular insulating member and the shell.

`A filling of cement is also used in this form as between the electrode and the tubular insulating member to tightly close them together.

In Fig. 3 I have shown a construction very similar to that shown in Fig. 2 except that the tubing insulator is relatively thicker and has an annular bevel 25 formed on its outer lower end portion that is iitted against an internal annular bevelled shoulder 26 formed in the lower end of the threaded portion of the outer shell Ill,

In this form the insulating tube would be placed in the casing from its upper end and secured against longitudinal movement by the positioning of the terminal. A lling of `cement I9 is also employed in this form as between the electrode and the insulating tubing to prevent gases from passing through the tube.

Fig. 4 is also constructed along the general lines of Figs. 2 and 3 and like those forms includes an insulating covering 2I that is threadably attached to the shell and is tapped to receive a threaded terminal member which is placed in the upper end above the insulating tube and is seated against the upper end of thel electrode. In this form the insulating tub'e does not extend clear down to the firing end of the shell I2 leaving a space to accomodate a head I6a on the end of the electrode forming an annular gap 21 between the end of the shell and forming a smooth surfaced lower end to the plug to expedite cleaning. This form of plug like those before described is also provided with a filling of cement I9 as between the electrode and the insulating tube. The insulating tube heretofore referred to is made of heat resisting glass, borosillica glass, quartz or may embrace other materials as equivalents Which have substantially the same functional characteristics when employed in the manufacture `of spark plugs.

From the description thus far it will be observed that in the operation of the present spark plug, the electrodes are arranged with relation to each other to provide the standard or desired gap and to the insulation interposed between them, so that the spark sweeps across the surface of the insulation, thus providing a path of reduced resistance. Also it has been foundthat the present spark plug possesses the ability to clean from the insulating surface soot, oil o r carbon which may deposit thereon, thus enabling the plug to be used under conditions in which prior plugs have quickly become fouled. The reasons for the self-cleaning feature of the present plug are not entirely understood, but it is believed that the corona which is undoubtedly formed and the accompanying corona .wind

assists materially in the removal of deposited I posed of an velectrically eilicient heat resisting glass such as the borosilica glass now commercially obtainable under the trade name Pyrex By the use of the term thin as employed in my claims, I intend to define a thickness of glass suiiciently small that the thickness of the insulating materials now commercially employed between the inner and outer electrodes in the manufacture of spark plugs for the same operating conditions at least is several times as great.

As a result thereof, elicient transfer of heat from the inner electrode to the outer member is accomplished.

The glass need only be sumciently thick to prevent it being punctured by the electrical potential applied between the innerv and outer electrodes. Furthermore, the glass is desirably of less thickness than the length of the spark gap between the electrodes as shown in Figure 3 but may be of a thickness somewhat greater than the length of the spark gap as shown in Figure 1.

' its inner end portion and having said bore of less By the use of the term heat resisting glass as employed in the claims, I intend to embrace quartz as well as borosilica glass such as .Pyrex,"

although obviously it is my intention to embrace.

'said member radially enlarged outwardly of its diameter toward the'outer end of the member, an inner electrode extending through said bore, a thin Walled tube of vitreous refractory insulating material in said bore about said electrode and of an external configuration corresponding with the internal configuration of said bore whereby not to be forced out of the bore by a pressure at the inner end of the plug, a cement seal between the electrode and the outer end portion of said tube, said tube of fused quartz whereby during use of the spark plug the tube at its outer end portion will remain cool enough for the effective use of cement as a seal between the electrode and the outer end portion of the tube, said tube terminating adjacent one end of the bore to provide a spark gap between said electrode and said member, and said tube having a wall thickness not substantially greater than the length of said spark gap.

2. A spark plug comprising an outer metallic member having an elongated bore therethrough, said member radially enlarged outwardly of its inner end to provide a wrench engageable portion, said member externally screw threaded on its inner end portion and having said bore tapering whereby it is of less diameter toward the outer end of the member, an inner electrode extending through said bore, a thin walled tube of vitreousrefractory insulating material in said bore about said electrode and of an external configuration corresponding with the internal configuration of said bore whereby not to be'forced out of said bore by a pressure at the inner end of the plug, a cement seal between the electrode and the outer end portion of said tube, said tube of fused quartz whereby during use of the spark plug the tube at its outer end portion will remain c'ool enough for the effective use of cement as a seal between the electrode and the outer end portion of the tube, said tube terminating adjacent one end of the bore to provide a spark gap between said electrode and said member, and said tube having a wall thickness not substantially greater than the length of said spark gap.

3. A spark plug comprising an outer metal member having an elongated bore therethrough, said member radially enlarged intermediateits ends and externally threaded at the inner and outer sides of said enlarged portion, an inner electrode extending through said bore, a thin walled tube of vitreous refractory insulating material in said bore about said electrode and extending beyond the outer end of said member and terminating adjacent the inner end thereof to provide a spark gap between the electrode and member, a cement seal between the electrode and the outer end portion of said tube, said tube of fused quartz whereby during use of the spark plug the tube. at its outer end portion-will remain cool enough for the effective use of cement as a seal between the electrode and the outer end portion of the tube, said tube having a wall thickness not substantially greater than the length of said spark gap, and a protective molded body of insulating materialI threaded to the outer threaded portion of -said metal member and disposed about the outer portion of said tube.

p 4.' 'Ihe combination'as in claim 3 including a terminal threaded into the outer end of said molded body and electrically connected with said inner electrode.

ROLLIN ABELL. 

